One form of semiconductor memory is the one time programmable (OTP) memory. One form of an OTP memory is an antifuse. An antifuse functions oppositely to a fuse by initially being nonconductive. When programmed, the antifuse becomes conductive. To program an antifuse a dielectric layer such as an oxide is subjected to a high electric field to generate a tunneling current through the dielectric. The tunneling current leads to a phenomenon known as hard dielectric breakdown. After dielectric breakdown, a conductive path is formed through the dielectric and thereby makes the antifuse become conductive.
Others have implemented antifuses in arrays having rows and columns to function as a nonvolatile memory (NVM) after being programmed. This type of memory functions as a read only memory (ROM) because the programming is irreversible. A conventional ROM is manufactured with a mask and thus the programming of the ROM must occur prior to manufacturing. In contrast, an antifuse is electrically programmed after the manufacture of the circuit and thus provides significantly more flexibility to users.
Typically capacitor structures are used as the dielectric material of the antifuse. A capacitor and a select transistor are commonly required to implement a single bit of information storage. The select transistor is required to select its associated particular capacitor for either a program or a read operation. Isolation elements are required at the boundaries of each bit in order to isolate the bits from each other. Therefore the area per bit is inefficient. As electronic devices evolve, an OTP memory which is smaller in area per bit is desired.
Others have implemented OTP memory using a crosspoint array which reduces cell size by using complex manufacturing processing requiring trenches having a significant depth and thus being hard to manufacture. The process complexity associated with known OTP memories is a significant factor in the cost of such OTP memories.
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